1. Field of the Invention
The invention relates to the use of certain N-vinyl amide polymers for use in controlling pitch in paper mill systems.
2. Introduction
The problem of pitch control in papermaking has previously been recognized. The pitch in the fibers of wood pulps is associated with naturally occurring lignin dispersing agents. Cooking and mechanical agitation which occur during the pulping by the sulfite process liberate pitch and these natural dispersing agents. However, as a result of the mechanical work on the fibers, the natural dispersing agents liberated along with the pitch are inadequate to keep the pitch from depositing on the equipment employed in beating, hydrating, refining, bleaching, and even on the wire used for forming the sheet. Because of the tendency of the pitch to agglomerate within the pulp suspension or deposit on the surfaces of the wire or other equipment, the pitch frequently causes the formation of spots or holes in the sheet formed. Additionally, the pitch may adhere to the wire or press rolls or dryer rolls and cause tearing of the sheet. The result of the pitch contamination is the production of sheets with numerous imperfections. Among other consequences of pitch deposition are the expense of cleaning the machinery frequently either with solvents or steam, and the loss of production during cleaning and replacing operations caused by breakdown of the sheet.
Cationic water soluble polymers are used commercially in the paper mills as pitch control agents. The present invention is predicated upon the discovery that certain water soluble lower alkyl N-vinyl amide polymers give colloidal pitch particle reduction in aqueous pulps.
The Invention
The invention consists of a process for controlling pitch deposition in pulp and papermaking systems. It comprises adding to the pulp a pitch controlling amount of a water soluble polymer which contains at least 5 mole percent of a lower alkyl N-vinyl amide or hydrolyzed lower alkyl N-vinyl amides. The lower alkyl N-vinyl amide polymers and the hydrolyzed lower alkyl N-vinyl amide polymers preferred for use in the practice of the invention have average molecular weights within the range of between 5,000-1,000,000. Preferably, the range is between 10,000 and 500,000.
The Lower Alkyl N-Vinyl Amide Polymers
The polymers used in the practice of the invention contain at least 5 mole percent of the lower alkyl N-vinyl amide. In most instances, the amount of the lower alkyl N-vinyl amide present in the polymer will be greater than 25 mole percent. The lower alkyl group of the N-vinyl amide usually contains from one to three carbon atoms. Illustrative of the lower alkyl N-vinyl amides that are present in the polymers used in the practice of the invention are N-vinyl formamide, N-vinyl acetamide and N-methyl(N-vinyl acetamide).
The other monomers present in the lower alkyl N-vinyl amide polymers may be selected from such monomeric groupings as N-vinyl amine, vinyl glycine, vinyl acetate, vinyl alcohol, acrylic acid, acrylamide and N-vinyl amides having alkyl groups containing between 12-22 carbon atoms. The amount of comonomer or termonomer present in the polymers of the invention often will be controlled by the method of preparation as well as effectiveness of a particular polymer in the control of pitch in a particular papermaking system.
The preparation of this polymer is frequently accomplished by the hydrolysis of a precursor lower alkyl N-vinyl amide polymer. Depending upon the degree of hydrolysis, the resulting polymer is either a polyvinyl amine (full or complete hydrolysis), or a polyvinyl amine copolymer of the starting lower alkyl N-vinyl amide which results from partial hydrolysis. Polymers containing vinyl alcohol groups are produced by the hydrolysis of lower alkyl N-vinyl amide/vinyl acetate copolymers. This hydrolysis often results in the production of vinyl amine groups as well as vinyl alcohol groups. Many of the lower alkyl N-vinyl amide copolymers are prepared using conventional polymerization techniques. Thus, the copolymers with acrylic acid or acrylamide are prepared in this fashion. These monomers typically are present in the copolymers in amounts ranging between 5 to 95 mole percent.
It is also possible to modify the polymers using organic modifying compounds such as alkylating agents to react with the vinyl amine containing polymers to produce secondary and tertiary amino groups. Typical is the use of chloroacetic acid to insert N-vinyl glycine groups into the molecule. Further, it is possible to insert fatty amide groups into the polymers by reacting N-vinyl amine groups with fatty acid chlorides which contain from 12-22 carbon atoms. Such a compounds is oleyl chloride.
To illustrate typical polymers used in the practice of the invention, Table 1 is presented below:
TABLE 1 ______________________________________ Polymer No. Polymer Chemistry MW ______________________________________ A Hydrolyzed p(vinylacetamide/ 60,000-150,000 vinylamine) Copolymer: 80-95% vinyl acetamide 20-50% vinyl amide B A modified with chloroacetate: 60,000-150,000 Mole % N-vinyl acetamide 80-95 N-vinyl amine 15-4} 20% of vinyl amine N-vinyl glycine 5-1} groups were modified with chloroacetate acid C A modified with oleyl chloride 60,000-150,000 Mole % N-vinyl acetamide 80-95 N-vinyl amine 17.5-2.5 N-vinyl oleamide 2.5 D Substantially hydrolyzed 1:1 10,200 p(vinyl acetate/N-methyl-N-vinyl acetamide) ______________________________________
In Table I, the mole percents and the molecular weight ranges were furnished by the supplier of the N-vinyl amide or hydrolyzed N-vinyl amide.